This invention relates generally to D.C. electrical circuits and more particularly to a novel means for protection of electrical circuits from electrical overloads and short circuits. The invention is especially useful in automotive electrical systems, and principles will be disclosed in connection with automotive electrical circuits.
The number of electrical circuits in automotive vehicles has increased over the years. In today's passenger cars and trucks, there are numerous electrical devices which are used for various purposes such as illumination, control, power, and instrumentation, for example. While the advent of electronics has given rise to major changes in automotive electrical systems, conventional forms of circuit protection devices, i.e., fuses and circuit breakers, continue to be used, and in increasing numbers as the number of circuits in the electrical systems increases. The common technique for providing protection against shorts, overloads, and other types of electrical problems or conditions is to include a circuit breaker or fuse in line, i.e., in series, with the wiring circuit being protected. The protected device can be the wire and/or electrical device. The necessity for having circuit protection devices is well documented and need not be explained here. With increasing numbers of circuits, and the correlative need for an increased number of protective devices, today's typical automotive vehicle comprises a panel devoted essentially exclusively to the mounting of most of these protective devices in a single location. The panel, or fuse block as it is sometimes called, comprises multiple compartments for the individual protective devices. Associated with these compartments are receptacles to provide for the replaceable mounting of the protective devices in the associated circuits. Accordingly, the panel comprises a large number of individual parts in assembled relationship, and it occupies a certain amount of space in an area of the vehicle where space is typically at a premium. A large number of wires attach to the panel to carry current to and from the various protective devices, and in order to serve the grouping of the protective devices in the panel, complexities must be introduced into the associated wiring harnesses.
Despite the advances which have taken place in the incorporation of electrical and electronic technology into today's automotive vehicle electrical circuits, they retain the fuse and circuit breaker panel concept with its attendant large number of individual protective devices to provide protection for the various individual circuits.
There are several ways to protect an electrical device without a circuit breaker or fuse, but most of the ways add several parts to the circuit and typically degrade the performance of the electrical circuit, such as by added voltage drop, higher power dissipation, etc. These protection methods are not known to enjoy any significant commercial use because of disadvantages such as those just mentioned.
The present invention relates to a novel means for protection of D.C. electrical cicuits which affords very significant advantages in automotive usage. One important advantage is that the fuse and circuit breaker panel concept of protection can be eliminated, thereby reducing the large number of individual circuit devices (i.e., fuses and circuit breakers) required to provide the protective function, and at the same time, freeing space because there is no longer a need for a separate panel.
The invention embodies the protective function in a semiconductor device sometimes commonly known as an intelligent switch. An intelligent switch comprises an internal controlled conduction path whose conductivity is controlled by an external control input. The switch contains another internal portion which monitors current flow through the main controlled conduction path and serves to internally interrupt the flow through the path in response to incipiency of current or temperature exceeding the rating of the main controlled conduction path.
The invention arises through the recognition that what is customarily considered in the art to be an electronic switch which has internal protection can also provide protection for the external components associated with it in a circuit branch such that separate external circuit protection devices are unnecessary in the branch. The invention possesses not only a generic aspect but also aspects which are specific to certain particular circuit embodiments. Various attributes will be seen in the several embodiments hereinafter disclosed.
The foregoing features, advantages and benefits of the invention, along with additional ones, will be seen in the ensuing description and claims which should be considered in conjunction with the accompanying drawings. The drawings disclose a preferred embodiment of the invention according to the best mode contemplated at the present time in carrying out the invention.